Bearing Monitoring: Determining the Causes of Bearing Failure

Preventing bearing failure ensures your organization stays up and running at peak efficiency. An effective bearing monitoring program requires you to understand the common causes and symptoms of bearing failure.

Healthy bearings are essential to reliable and energy-efficient machine operation. A single bearing failure has the potential to cause a full equipment shutdown, resulting in many hours of lost production time.

An effective bearing monitoring program will help you prevent bearing failures across a wide range of assets, ensuring your organization continues operating at peak efficiency.

An Analysis of Bearing Failure

Every year, an estimated 10 billion bearings are manufactured worldwide. But only a small percentage of bearings experience failure. In fact, some 90% of bearings outlive the equipment they are installed in. Most of the remaining bearings are replaced prior to failure thanks to effective bearing monitoring and preventive maintenance strategies.

That leaves 0.5% of bearings that must be replaced either due to irreparable damage or failure. That still means some 50 million bearings around the world must be replaced every year due to damage or failure. Bearing failures can result in lost productivity and time, and sometimes even cause entire plants to be shut down.

To ensure your organization has an effective bearing monitoring program, you need to understand the common causes and effects of bearing failure, as well as the most effective strategies for monitoring and preventing bearing failure.

Common Causes of Bearing Failure

There are several common reasons why bearings fail or get damaged. The most common bearing failure modes include fatigue, deformation, lubrication failures, corrosion, electrical damage, and incorrect design. Generally speaking:

• One-third of bearing failures are due to fatigue.
• One-third of bearing failures are due to lubrication problems (incorrect lubricant choice, quantity, or interval).
• A small percentage of bearing failures are due to contamination (ineffective seals).
• A roughly equal small percentage of bearing failures occur for other reasons (improper handling and mounting, excessive loads, wrong fits, etc.).

Based on the above bearing failure analysis, it’s clear that fatigue and improper lubrication should both be considered primary concerns in any bearing monitoring program.  

Detailed Causes of Bearing Failure

Here’s a closer look at the common causes of bearing failure:

Fatigue

Bearing failure is often caused by fatigue, which happens when bearings are subject to excess stress. Misalignment, insufficient lubrication, and contamination can all contribute to bearing fatigue. All of these factors cause repeated stress on the bearing material, creating flaking, spalling, and microscopic cracks to form in the bearing material. Over time, the cracks grow, and the bearing eventually fails.

Lubrication Issues

Improper lubrication is one of the leading causes of bearing failure. That could mean insufficient lubrication, which contributes to bearing fatigue. It could also mean you’re using the wrong lubricant. In some cases, high temperatures can degrade the lubricant.

The early warning signs of faulty lubrication include discoloration on the rolling elements and tracks, and well as overheated bearings.

Misalignment

Another frequent cause of bearing failure is misalignment. It’s a best practice to align assets at the installation stage, and then re-check at regular intervals, since factors like thermal growth and vibration can cause misalignment over time. Laser tools are the gold standard for checking alignment.

Improper Installation

Faulty installation and mounting also cause bearings to fail. Make sure to install bearings using the correct tools, including heat where appropriate, so that they fit correctly without being forced. Operators should also check for proper alignment during the installation stage. Finally, the bearings and housing should be thoroughly cleaned and lubricated during installation.

Excess Loads

Excess loads cause undue wear and tear on bearings as the result of increased friction between the rolling element and the raceway. Excessive loads cause heavy wear paths, overheating, and overall machine fatigue, leading to bearing failure.

Contamination

Dirt, debris, and chemicals can all contaminate bearings and cause deterioration. Over time, this leads to corrosion and bearing failure. Seal failure, which leads to contamination, can be the result of improper installation. Misalignment can also contribute to seal failure and contamination.

Bearings contaminated with dirt and debris often have dented rolling elements and higher-than-usual vibration levels.

Incorrect Fit

Installing bearings with the right fit is very important. An overly tight fit can cause stress and friction; it usually causes a visibly heavy rolling element wear path. An excessively loose fit, on the other hand, results in vibration and noise, which can also lead to bearing failure and serious faults over time.

Symptoms and Identification of Bearing Failures

If a damaged bearing isn’t replaced in time, it can cascade into a host of problems for equipment and components. Fortunately, the early signs of bearing failure are easy to spot, especially with the right equipment. Condition monitoring tools, like vibration analyzers and sensors, are a highly effective way to track the first bearing failure symptoms that cause machine damage.

High Vibration Levels

The first sign of bearing failure is an increase in machine vibration. At this stage, the bearings still function normally, but the change in vibration patterns indicates a developing fault. A good vibration sensor can pick up on the early warning signs and issue alerts when vibration levels cross a preset threshold.

High Temperature and Noise

Vibration levels will grow progressively more intense as the bearing deteriorates. If left uncorrected, bearing damage causes dramatic temperature increases due to friction between the damaged bearing and component parts. At this point, the machine will start to make noise and may visibly vibrate.

Visible Damage

As the bearing deteriorates further, it will begin to show pitting and spiraling. Cracks will appear on the raceway or on the bearing itself. At this stage, crews need to take action urgently to prevent damage to components or nearby machines. At its worst, bearing failure can cause critical assets to shut down and freeze production at the plant, leading to expensive downtime and productivity losses. Fortunately, there are preventive measures crews can take to avoid bearing failure.

Preventive Measures to Avoid Bearing Failures

Most of the time, bearings are reliable and have a long service life. For that reason, one of the most important preventive maintenance tasks is to regularly remove and replace bearings. Keeping these tasks on a schedule can prevent unplanned downtime and costly repairs.

There are also some simple preventive measures that can stop premature wear and tear on bearings.

At the installation stage, ensure that you’ve correctly mounted each bearing. Verify the shaft and housing tolerances and maintain the radial internal clearance set out in the original design. Check to make sure that you’ve correctly sealed the bearings so that they stay protected from dirt, debris, or water. Also, remember to properly lubricate each bearing.

It’s important to check machine alignment during the installation stage and then re-check it regularly. Over time, misalignment happens gradually and can destroy bearings when left unattended. For best results, verify alignment using a single-laser alignment tool, which quickly identifies even minor alignment faults that damage bearings.

Maintain proper lubrication throughout the bearing lifespan. This is a careful balancing act. Too much lubrication causes bearings to stick, but too little lubrication leads to high levels of friction, damaging the components. It’s also critical to use the lubricant and lubrication schedule recommended by the manufacturer.

What Happens if a Bearing Fails?

When a bearing fails – whether due to fatigue, improper lubrication, damaged seals, or something else – it doesn’t just mean the bearing needs to be replaced. A single bearing failure can cause a cascading chain reaction that can bend shafts and cause major damage to other coupled equipment. Bearing failures can even put workers at risk of harm.

Fortunately, many common bearing issues can be identified long before they become major problems. And that’s largely thanks to the distinct vibration measurement patterns they produce during normal operation. When that vibration changes, it’s the first sign of a problem. As long as you have the tools in place to catch the variance from normal vibration levels, you can easily get ahead of bearing failure.

What are Traditional Bearing Monitoring Techniques?

Ensuring bearings meet or exceed their operational lifetimes depends on a number of factors, including bearing quality, storage, and stocking practices, proper mounting and lubrication, effective sealing, and use in the appropriate operating conditions. Traditional bearing condition monitoring techniques largely relied on three main methods, all related to human senses:

• Visual monitoring (sight)
• Audible monitoring (sound)
• Vibration monitoring (touch)

In the past, maintenance and repair technicians looked for, listened for, and felt for early warning signs of bearing failure. However, manual methods are always prone to error. Fortunately, with the advanced sensitivity of modern condition monitoring sensors, you can more easily detect extremely early warning signs of potential bearing failure that the human senses might miss.

Online condition monitoring systems also can be deployed to instantly track and record the real-time data captured by such sensors, helping your organization carry out an effective bearing condition monitoring strategy.

What is Bearing Condition Monitoring?

Although fatigue and improper lubrication are two of the most common causes of bearing failure, they are also rather straightforward to spot before they become major problems. You simply need to deploy an effective bearing condition monitoring program.

There are many types of condition monitoring tools you can use to stay ahead of preventable maintenance problems. For example, power monitoring measures fluctuations in current, voltage, and frequency, alerting you to changes in the energy usage of your assets. In addition to causing unnecessary wear and tear, such energy fluctuations may also point to safety concerns that should be immediately addressed.

An effective condition monitoring program for bearing failure typically relies on sensors and hand-held devices to precisely measure the “vital signs” of your assets, including power usage, vibration frequency, temperature, and much more.

These electronic devices allow you to continuously track the health of your machines, alerting you to any faults or abnormalities early on so that you can make repairs and avoid costly unplanned downtime. One especially powerful group of bearing monitoring tools is vibration sensors.

How to Use Vibration Sensors for Bearing Monitoring

An effective bearing monitoring program usually includes vibration monitoring, as changes in vibrations are often the first sign of future bearing failure. By measuring the intensity and frequency of vibrations, handheld, wired, or wireless vibration sensors can detect and alert you to abnormal readings months before it becomes a serious problem. This gives you the time you need to effectively plan downtime to carry out the necessary preventative maintenance.

What are the Benefits of Bearing Condition Monitoring?

By carrying out a bearing condition monitoring program, you can help ensure your organization’s maintenance strategy is preventive rather than corrective. This means you will catch problems before they result in asset failure, reducing maintenance costs and increasing productivity.

Fortunately, today’s modern technology makes carrying out an effective bearing monitoring program easier and more cost-effective than ever. Advances in both sensors and software mean that deploying a cutting-edge conditioning monitoring program is not only feasible, it is a smart financial decision, helping you cut costs and increase uptime.

In other words, organizations that have a strong bearing conditioning monitoring program will not only stay ahead of bearing failures, they’ll also stay ahead of the competition.